Instrument for adjusting range-finders.



A. BARR 6: WuSTROUD. INSTRUMENT FOR ADJUSTING RANGE'IINDERS.

APPLICATION FILED 001. 24, 1907.

Patented Sept. 14, 1909.

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A. BARR & W. STROUD.

INSTRUMENT FOR ADJUSTING RANGE FINDERS.

APPLICATION FILED OCT. 24, 1907.

Patented Sept. 14, 1909. 3 SHEETSf'SHEET 2.

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A. BARR & W, STROUD. INSTRUMENT FOR ADJUSTING RANGE FINDERS.

APPLIUATION FILED OUT. 24, 1907.

Patented Sept.,14, 1909.

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ANDREW 5 cm to. PHmUYIICGRAFiERB, WASHINGTON. D. a

UNITED sTAans PATENT o Aitc'HrBALn BARE, F GLASGOW; soo'rLAND, ANDWILLIAM s'raonn, or LEEDS, ENGLAND.

Specification of Letters Patent.

Patented Sept. 14, 1909 Application filed October 24, 1907. Serial No.399,016.

To all 'wlwm it may concern:

Be 1t known that we, ARGHIBALD BARR, of Glasgow, Scotland, and WILLIAMSTROUD,

' of Leeds, England, have invented certain new and useful Improvementsin Instruments for Adjusting Range- Finders, of which the following is aspecification.

Our invention relates to means for adjusting rangefinders and the objectof our invention is to provide appliances in connection with singleobserver rangefinders working on either the coincidence or stereoscopicprinciple, to enable the operator to put the rangefinder into correctadjustment, when necessary, without observing upon a celestial object oran object whose range is known. This we accomplish in the followingmanner :IVe provide (1) two lenses L and L of equal or nearly equalfocal length upon each of which a fine line, or other suitable mark, ismade, and (2) a pair of optical squares, P and I. The two lenses aremounted up at a distance apart equal to their common focal length. Theline upon L (suitably illuminated) is thus situated at the principalfocal plane of L and the line upon L (also illuminated) is situated atthe principal focal plane of L Thus the light coming from a point of themark upon L will furnish a parallel beam of light emerging from L andsimilarly that coming from a point of the mark upon L will furnish aparallel beam of light emerging from L We shall suppose at first thatthe marks are so placed on the lenses that the central axes of thesebeams of light are parallel to one anothera condition which would besatisfied if the points referred to coincided with the optical centersof the lenses. If this is the case then the two emerging beams willstill remain parallel, notwithstanding any small shift of the lenses Lor L in the plane at right angles to the principal axes of the lenses.To enable these parallel beams of light. to enter the rangefinder, oneof the optical squares P is placed opposite a portion of oneend-reflector of the rangefinder and the other P opposite a portion ofthe other end-reflector, and the two lenses L L are so placed relativelyto the optical squares that light coming from the mark on L emerges as aparallel beam from the lens L and is turned through 90 by the opticalsquare P and finally enters the end-reflector of the rangefinder;similarly light coming from the mark on L emerges as a parallel beamfrom the lens L and is then turned through 90 in the optical square Pand finally enters the other end-reflector of the rangefinder. If, as wehave supposed the central axes of these beams are parallel to oneanother, then the beams of light entering the rangefinder will virtuallycome from one point at infinity, in other words we are provided with anartificial infinity. The marks may conveniently take the form of lineson the lenses, at right angles to the plane of triangulation of therangefinder. Even if these lines are so placed that the beams from themare not parallel to each other in the plane of triangulation on emergingfrom the lenses, we still have the equivalent of one line situated at agiven distance from the rangefinder. In some cases the marks may not bemade directly on the lenses L and L but may be securely attached to thelenses. emay sometimes insert in thepath of the beams a refracting'prism of suitable angle capable of rotation about an axis perpendicularto its face or nearly so. Such rotation will produce an alteration ofthe angle between the central axes of the two beams in the plane oftriangulation and can therefore be used to adjust the two beams so as tobe parallel in the plane of triangulation and thus to produce anartificial infinity even if the marks on the lenses are not coincidentwith the optical centers of the lenses, or if the optical squares P andP do not set out angles of exactly 90.

The various parts of this adjusting instrument may be mounted on aseparate frame detachable from the rangefinder when not in use, or anyof the various parts may be attached to the framework of the rangefinderitself.

In some types of rangefinders and in some arrangements of the parts ofthe adjuster the adjusting marks will appear in coincidence only whenthe operating mechanism of the rangefinder is set to read infinity orother chosen range, in other cases the an rangement may be such that themarks will appear in coincidence whatever the rangefinder be set toread, if the rangefinder is in correct adjustment.

In order that the nature of our invention and the manner in which thesame may be performed may be more clearly and fully understood, we shallnow describe it with reference to the accompanying drawings and to theletters and marks thereon.-- v l v Figure l is an elevation and Fig. lis a plan of a rangefinder with the adjusting instrument in positionrelatively thereto.- Fig.v

2 and Fig. 3 are cross sections of the rangefinder and ad ustinglnstrument. Fig. lis a sectional elevation of one end portion of theadjusting instrument; Fig. 5 is an en larged View of one of theobjectives and of the adjusting instrument with the mark rangefinder,but -as will be explained belowthe adjuster maybe incorporated in thesame case as the rangefinde'r, and one example of thisis illustrated inFigs. 8 and 9. 1n the first instance we shall suppose that therangefinder'works upon the coincidence principle.

Iii-Figs. 1 to 4, A represents a rangefinderand G a tube containing theoptical parts of the adjuster. A and G are shown broken to save room inthe drawings. B B are the windows through which the beams of light fromthe distant object enter the range finder. C is a tube or framepiececarrying the optical parts of the adjuster. L L are two lensesor'objectives of equal focal length, orvery nearly so, set at a distanceapart equal to their focal length, or nearly so. E and E, are smallreflecting prisms sending'beams of light from lamps F F (or othersources of'light), through the objectives, which carry, oppositethe'prisms E E marks G G conveniently consisting of vertical lines andcircles as shown in Fig. 5,

thouglr the type of marks used may be varied as may be found convenient.The

marks may conveniently be out on films of black varnish covering a smallpart ofone surface of each objective so as to show as bright lines inthe field of the rangefinder, but they may be formed in any other mannerso long as they are fixed relatively to the objectives to which they arecontiguous; P P5 are optical squares represented as being of the Prandlprism form though other forms may be used.

The principle of'the instrument will be understood by reference to Fig.7 The mark G (considered as a point) being set at" the principal focusof the lens L and illuminated by light from the lamp F (Figs; 1 and l)reflected by the prism E (Figs. 1, 1 and 4-) will emit a beam'ofdivergent rays which are rendered parallel,

ornearly-so, by the lens L andso are trans- 'mitted' by the opticalsquare P to the range finder as if the-rays camefro-m avery. dis: tantobject. A similar beam of light entersthe other end of the rangefinderfrom the mark G tl16"0bjeCtlV6 L and the optical square P It will beseen that if the parts are suitably arranged relatively to eachother thetwo beams, entering the rangefinder by the windows B B will virtuallycome from one object of the form Gr set an infinite distance in front ofthe rangefinder, and thus artificial infinity by aid of constituteanwhich the adjustmentfof; the range-finder may be-tested,'and by soadjusting therangefinder that it reads infinity when the images ofthe-marks are seen in correct alinement in the rangefinder field, therangefinder may be put into correct adjustment. In Fig. (5, forclearness, the images are shown out of coincidence which willindicatethat the rangefinder is not in correct adjustment if therangefinder scale is meantime indicating infinity V V It is notessential that the-beams entering the windows-B and 13 shouldbe'parallel to each other; the optical parts of the adj uster= may beset sothat the beams virtually come from an ob ect Gr set at anychosenvirtual distance in front*oftherangefinder, and so long as thisvirtual'distance is known the rangefinder may be adjustedby making-itread this virtual distance when theimages oi the marks are seen incorrect alinement iirthe rangefinder field.

In some-cases we place a retracting distance of'the marks is trulyinfinity? or.

other chosen distance, irrespective of any want ofaccurate setting ofthe other parts of the apparatus orany deviation of the angles set outby the optical squares P After the adjusterfrom true right angles. hasbeen so adjusted the prism J may be fixed. Should the marks G G, beplaced one to one side and the other to the other side of 'the centersof the objectives, the

beams entering" the range finder windows would still be parallel butoblique, so as to causethe image of the marks toyappear to justerrelatively to the rangefinder.

The'adjuster wil-lnotbe deranged by any small movements of either of theobjectives L L relatively to the other parts of-the apparatus. If forexample'theadjuster-is arranged to indicate infinity and the objec-'tive L carrying the mark G with it, were prism- J of small angle ofdeviation in the paths 105 This prism therefore en- 7 L, or any bendingof the adjuster moved nearer to the r'angefinder in the plan (Fig 1) itwill be seen that this would cause the axis of the beam from G, throughthe optical center of the lens L to take a direction somewhat oblique tothe rangefinder but the optical center of the lens L would be equallymoved so that the axis of the beam from G through the optical center ofL would take an equally oblique direction and thus the two beamsemerging from the objectives would still be parallel to each other. Anysmall movement of the objectives L tube C therefore produces no effectupon the virtual distance of the marks from the rangefinder.

In order to minimize any effect from temperature changes on the anglesset out by the optical squares P P we prefer to make these of the Prandlprism form (as shown in Figs. 1 and 7) and to make them small comparedwith the reflectors of the rangefinder.

The adjuster may be so arranged that when in place it excludes all lightfrom the rangefinder field except that coming through the adjuster. Inother cases we may arrange that the optical squares of the adjuster comein front of portions only of the reflectors of the rangefinder so thatthe images of the marks may be visible in the rangefinder field whilethe rangefinder is being used to observe upon a real object.

In some rangefinders the appliances for effecting the deviation of oneor both of the beams of light by which a distant object is viewed in theoperation of the rangefinder, are placed outside the end reflectors. Insuch cases the optical squares of the adjuster may be set between suchdeviating appliances and the end reflectors of the rangefinder, and theapparent coincidence of the adjuster marks will not be affected by theworking of the operating mechanism of the rangefinder. In this case,when the adjuster and rangefinder are once adjusted, the images of themarks should appear in coincidence whatever be the range indicated bythe rangefinder scale. Figs. 8 and 9 represent such an arrangement.Corresponding parts of the adjuster are lettered in accordance with thedescription given above, and the operating prisms of the rangefinder areshown at D D It will be obvious that the adjuster can be equally wellapplied to instruments work-- ing upon the stereosco ic principle. Inthis case the two images of the marks G G will be seen in the twoeyepieces respectively and the rangefinder will be in correct adjustmentwhen the virtual object Gr appears to be at the same distance as thereference marks in the rangefinder with which the apparent distance ofan object is compared, the rangefinder scale being suitably set. Thus ifthe adjuster is placed outside of the rangefinder, and adjusted to givean artificial infinity, the virtual object G should appear to be at thesame distance as the reference marks when the rangefinder scale readsinfinity. In the case of a stereoscopic rangefinder, as in that of acoincidence rangefinder, the adjuster may be set to make the virtualobject G be at any desired virtual distance from the rangefinder, whenthe virtual object G and the reference marks used in the rangefindershould appear to be at the same distance when the rangefinder scale isset to read the distance of the virtual object Gr.

Claims.

1. In an instrument for adjusting range finders, the combination of twoobjectives of approximately the same focal. length and provided withsuitable marks; and a pair of optical squares whereby beams of light areconveyed from the marks to the rangefinder.

2. In an instrument of the character described, the combination of anadjuster provided with two objectives; and a refracting prism mountedbetween said objectives and adapted to be rotated about an axiscoincident with the axis of the beams of light passing between theobjectives.

In witness whereof we have hereunto set our hands in the presence of twowitnesses.

ARCHIBALD BARR. WILLIAM STROUD.

Vitnesses JOHN LIIJDLE, JOHN T. LIDDLE.

